1. Field of the Invention
The present invention relates to a motor driving circuit and method, and more particularly, to a motor driving circuit and method capable of reducing power consumption and avoiding continuous generation of reverse current.
2. Description of the Prior Art
A direct-current (DC) motor driver is a necessary power transformation device in modern industries, which is capable of transforming electrical energy into kinetic energy required for driving devices. Conventional motors include DC motors, AC motors, and stepping motors. DC motors and AC motors are often applied in products which do not require particularly delicate manipulation, for example, blades of an electric fan are usually rotated by utilizing a DC motor or AC motor. In recent years, how to design motors with better performance has become a major objective in the industry.
Please refer to FIG. 1, which is a schematic diagram of a conventional motor driving circuit 10. The motor driving circuit 10 includes a power supply 100, a protection diode D1, a Hall sensor 110, a control unit 120, a driving circuit 130 and a motor load Le. The power supply 100 is utilized for generating an input voltage Vin. The protection diode D1 is coupled to the power supply 100, for protecting the power supply 100 and avoiding power source reversal connection which may burn down the entire integrated circuit. The Hall sensor 110 senses locations of the magnetic poles of the motor load Le for generating a first time sequential control signal H+ and a second time sequential control signal H− according to the working characteristic of the motor load Le. The control unit 120 is coupled to the Hall sensor 110, for receiving the first time sequential control signal H+ and the second time sequential control signal H−, and generating a first transistor control signal CTRL_1, a second transistor control signal CTRL_2, a third transistor control signal CTRL_3 and a fourth transistor control signal CTRL_4 accordingly, so as to control the driving circuit 130. In detail, the driving-stage circuit 130 includes an input terminal 132, a first output terminal 134, a second output terminal 136, a first transistor Q1, a second transistor Q2, a third transistor Q3 and a fourth transistor Q4. The input terminal 132, which is coupled to the protection diode D1, is used for receiving the supply voltage VDD. The first output terminal 134 and the second output terminal 136 are used for outputting a first output voltage Vout1 and a second output voltage Vout2, respectively. The first transistor Q1, which is coupled to the control unit 120, the input terminal 132 and the first output terminal 134, is used for switching the conduction condition between the input terminal 132 and the first output terminal 134 according to the first transistor control signal CTRL_1. The second transistor Q2, which is coupled to the control unit 120, a grounding terminal 138 and the first output terminal 134, is used for switching the conduction condition between the first output terminal 134 and the grounding terminal 138 according to the second transistor control signal CTRL_2. The third transistor Q3, which is coupled to the control unit 120, the input terminal 132 and the second output terminal 136, is used for switching the conduction condition between the input terminal 132 and the second output terminal 136 according to the third transistor control signal CTRL_3. The fourth transistor Q4, which is coupled to the control unit 120, the grounding terminal 138 and the second output terminal 136, is used for switching the conduction condition between the second output terminal 136 and the grounding terminal 138 according to the fourth transistor control signal CTRL_4. Each of the first transistor Q1, the second transistor Q2, the third transistor Q3 and the fourth transistor Q4 can be either a P-type metal-oxide-semiconductor (MOS) transistor or an N-type MOS transistor. In FIG. 1, the first transistor Q1 and the third transistor Q3 are P-type MOS transistors, while the second transistor Q2 and the fourth transistor Q4 are N-type MOS transistors. Those skilled in the art know that the above configuration for the first transistor Q1, the second transistor Q2, the third transistor Q3 and the fourth transistor Q4 in FIG. 1 is merely one example of possible configurations. The motor load Le, which is coupled to the first output terminal 134 and the second output terminal 136, is used for generating a motor current IL according to the first output voltage Vout1 and the second output voltage Vout2. When the motor current IL is positive, the direction of the motor current IL is from the first output terminal 134 to the second output terminal 136; otherwise, when the motor current IL is negative, the direction of the motor current IL is from the second output terminal 136 to the first output terminal 134.
Please refer to FIG. 2, which is a timing diagram of the first time sequential control signal H+, the second time sequential control signal H−, the first output voltage Vout1, the second output voltage Vout2 and the motor current IL shown in FIG. 1. When the voltage level of the first time sequential control signal H+ decreases to the first transition voltage VH+, the first output voltage Vout1 switches from a high voltage level to a low voltage level; when the voltage level of the first time sequential control signal H+ continues decreasing to the second transition voltage VH−, the second output voltage Vout2 switches from the low voltage level to the high voltage level. If the first transition voltage VH+ is set too low, a large amount of power consumption may be generated during the reverse current absorption stage (the period in which the voltage level of the first time sequential control signal H+ decreases to the second transition voltage VH− and the motor current decreases to zero) due to over-high motor current IL when the voltage level of the first time sequential control signal H+ decreases to the second transition voltage VH−, causing waste of electrical energy and even burn-down of the motor driving circuit 10.
In order to solve the aforementioned problem, the prior art provides a method of adjusting the first transition voltage VH+ higher to overcome generation of a large amount of power consumption during the reverse current absorption stage which causes waste of electrical energy and burn-down of the motor driving circuit. Please refer to FIG. 3, after adjusting the first transition voltage VH+higher, the motor current IL can be lower when the voltage level of the first time sequential control signal H+ decreases to the second transition voltage VH− because the time interval for the voltage level of the first time sequential control signal H+ to decrease to the first transition voltage VH+ and to the second transition voltage VH− is prolonged. Therefore, the power consumption can be effectively reduced when entering the reverse current absorption stage.
However, according to the aforementioned method, the motor current IL may decrease to zero too early during a situation that the speed of the motor load Le slows down or the motor current IL is over-low, such that the reverse current is generated, causing the problems that the working efficiency of the motor load Le becomes worse and noise is easily generated. Please also refer to FIG. 4, during the period that the voltage level of the first time sequential control signal H+ decreases to the first transition voltage VH+ and to the second transition voltage VH−, the motor current IL decreases to be lower than zero, causing the motor load IL to do negative work, and thus the working efficiency of the motor load Le becomes worse.
The aforementioned problems can be resolved by adjusting the first transition voltage VH+ lower again. However, the first transition voltage VH+ should be adjusted according to different conditions, and the prior art does not provide a mechanism of adaptive switching the transition voltage VH+. For the above reason, an improvement over the prior art is needed.